1. Field of the Invention
The present invention relates to a liquid crystal light modulating device, and more particularly to a liquid crystal light modulating device wherein at least one of two substrates is flexible. The present invention also relates to a method and an apparatus of such a liquid crystal light modulating device.
2. Description of Related Art
Recently, a display device which uses a liquid crystal composition is used as not only a display section of a note type personal computer but also display sections of other various display media. Such a liquid crystal display device has an advantage of contributing to energy saving and thinning of an apparatus. Therefore, liquid crystal display devices of a medium size and a small size have been employed in portable equipment. In these days, however, liquid crystal display devices are being developed to be used as large size displays which are substitutes for CRTs and displays of wall type TVs.
As a method of manufacturing a liquid crystal display device, conventionally, a vacuum injection method has been adopted. In this method, on one of a pair of glass substrates, which have electrodes thereon, sealing resin is provided at the sides while making an opening through which a liquid crystal composition is to be injected. On the other substrate, spacers are dispersed so that a specified gap can be maintained between the two substrates. Thereafter, the substrates are laminated and heated, whereby the sealing resin is hardened. Thus, a panel is fabricated. This panel is disposed in a decompressed bath, and the inside of the panel is evacuated. In this state, the opening is made contact with a liquid crystal composition. Then, by returning the bath into the atmospheric pressure, the liquid crystal composition is injected into the panel.
According to the vacuum injection method, however, as the display area is increasing, a larger injecting device and a longer injecting time are required. Therefore, another efficient method of injecting and sealing a liquid crystal composition in a panel was demanded.
Measures to solve this problem have been suggested in Japanese Patent Laid Open Publication Nos. 61-190313, 5-5890, 5-5892, 5-5893, 8-171093, 9-127528, 9-127528, 9-211437. According to the methods disclosed by these publications, a liquid crystal display device is fabricated as follows: first, sealing resin is formed on a substrate, and a liquid crystal composition is dropped on the substrate; next, another substrate is pressed against the substrate in such a way to have a specified gap between the substrates; then, the sealing resin is hardened. According to these methods, vacuum injection is not necessary.
These methods, however, have problems. In the method disclosed by Publication No. 61-190313, when the gap between the substrates becomes even while the substrates are pressed, the sealing resin is hardened. The substrates are likely to be displaced from each other while being pressed because the liquid crystal composition which was dropped inside the sealing resin is fluid and because the sealing resin has not been hardened. Also, while the sealing resin is being hardened thereafter, the substrates may be displaced further. Thus, in this method, there are still problems different from those in the vacuum injection method.
In either of the methods disclosed by Publication Nos. 5-5890, 5-5892 and 5-5893, a liquid crystal composition is dispensed onto a substrate with unhardened sealing resin. Thereafter, another substrate is laid and pressed on this substrate, and the sealing resin is hardened. Thus, because the sealing resin has not been hardened when the liquid crystal composition is dispensed onto the substrate, the above-described problems are likely to occur. In the methods disclosed by Publication Nos. 5-5892 and 5-5893, the substrates or the sealing resin has a portion through which an excess of the liquid crystal composition will be discharged outward when the two substrates are laminated. As mentioned, thereafter, the sealing resin is hardened. After the sealing resin is hardened, there is still the discharging portion. Therefore, when the pressure applied to the substrates is reduced after the lamination of the substrate, the substrates expand, and the gap between the substrates cannot be adjusted exactly to the designed one. Thus, in these methods, there is still a problem different from the problems in the vacuum injection method.
In the method disclosed by Publication No. 8-171093, photosetting resin is used as the sealing resin, and before the sealing resin is hardened, two substrates are laminated. Therefore, in this method, there are still the above-described problems caused by applying pressure between unhardened sealing resin and a liquid crystal composition. Further, according to this method, after the gap between the substrates was adjusted, ultraviolet rays are radiated in vacuum. At this time, it is necessary to press at least the substrate which is directly exposed to the ultraviolet ray radiation uniformly with a plate which transmits ultraviolet rays. The surface of the plate must be sufficiently flat. It is, however, difficult to produce such a plate when the substrates are large.
In the method disclosed by Publication No. 9-127528, thermoplastic photosetting resin which has a softening point within a range from a room temperature to the N-I point of the liquid crystal composition is used as the sealing resin. Generally, the N-I point of a liquid crystal composition is at most around 100° C., and a material which has a softening point less than 100° C. is used as the sealing resin. In this case, the sealing resin may softened when it is exposed to heat radiated from a back light or when it is used in a closed room or a car. If the sealing resin becomes soft, the resin may fuse into the liquid crystal composition and may form a thin film on the interfaces between the liquid crystal composition and the substrates, thereby lowering the reliability of the display and making the liquid crystal out of alignment.
In the method disclosed by Publication No. 9-211437, a liquid crystal composition is dispensed on a substrate, and another substrate is laid thereon while being bent. Thereafter, ultraviolet rays are radiated. Thus, in-polymer dispersed liquid crystal is made. Prior to the lamination of the substrates, a seal with an opening is provided to one of the substrates, and after the substrates are laminated, the seal is exposed to light to be hardened. However, a step of closing the opening of the seal is necessary, thereby complicating the manufacturing process. Also, there are still the above-described problems caused by using unhardened resin, radiating ultraviolet rays after lamination of substrates.
Further, none of the above publications discloses an apparatus which is suited to mass-produce liquid crystal light modulating devices.